Hack history / 2026 / Hack or exploit
Balancer V1
Hack or exploit on Aug 31, 2026 · Rounding Error
IN REVIEWSOURCES DISAGREE ON DATE OR LOSS · 3 SOURCES
Lost
$234K
sources: $111K to $234K
Returned
none listed
as the sources state it
Rank
#1,436
among thefts by dollars lost
What happened
An attacker first used swaps to reduce the Balancer V1 BPool’s WBTC reserve to near-dust levels, then exploited rounding in joinswapPoolAmountOut. When the function reverse-calculated the WBTC required to mint a caller-specified amount of BPT, 18-decimal fixed-point arithmetic rounded the required input down to 1 satoshi while still minting the full BPT amount. The attacker minted 4,408.8 BPT through these underpriced joins and exited the pool proportionally to drain DPI, USDC, WETH, and WBTC
In review: possible duplicate within one source; sources disagree on the loss.
Details
- Date
- Aug 31, 2026
- Kind
- Hack or exploit
- Method
- Rounding Error
- How in
- Smart contract bug
- Target
- DeFi protocol
- Chains
- Ethereum
Reported by
Related incidents
Balancer V1 2026 · Hack or exploit · $250K
Balancer V2 2025 · Hack or exploit · $120.5M
Balancer V2 2023 · Hack or exploit · $238K
Balancer V2 2023 · Hack or exploit · $2M
Balancer 2023 · Hack or exploit · $11.9M
Balancer V2 2025 · Hack or exploit · $120.5M
Balancer V2 2023 · Hack or exploit · $238K
Balancer V2 2023 · Hack or exploit · $2M
Balancer 2023 · Hack or exploit · $11.9M
Cite this page
SwanBluechip, "Balancer V1 hack, Aug 31, 2026: $234K lost", Crypto hack history, https://swan-hack-tracker.pages.dev/history/i/ht750db5be6b/ (data as of 2026-10-31).